Martensitic steel
The invention relates to a steel for structural components used at elevated temperatures. The steel comprises the following main components (in wt. %): Cr 8.0-14.0 Ni 4.0-14.0 Al 2.5-5.0 C 0.003-0.3 N≤0.06 Mo+W≤4.0 at least one of: Nb 0.01-1.0 Ta 0.01-1.0 Ti 0.01-1.0 Zr 0.01-1.0 Hf 0.01-1.0 Y 0.05-1.0 balance optional elements, Fe and impurities; and the steel composition fulfilling the following condition: Cr(eq)+Ni(eq)≤30; where Cr(eq)=Cr+2Al+1.5(Si+Nb+Ti)+Mo+0.5W; and Ni(eq)=Ni+10(C+N)+0.5(Mn+Cu+Co).
1. A steel comprising of in weight % (wt. %):
Cr 8.0-14.0
Ni 4.0-14.0
Al 2.5-5.0
C 0.003-0.3
N≤0.06
Mo+W≤4.0
at least one of:
Nb 0.01-1.0
Ta 0.01-1.0
Ti 0.01-1.0
Zr 0.01-1.0
Hf 0.01-1.0
Y 0.05-1.0
optionally
Si≤2.0
Mn≤ 4.0
Cu≤ 4
Co≤2
V≤1
B≤0.1
Bi≤0.2
Se≤ 0.3
Ca≤ 0.01
Mg≤ 0.01
O 0.02-0.50
RE≤ 0.3
balance Fe apart from impurities, wherein the content of RE does not include the amount of Y but only the amount of the elements having the atomic number 21 and/or any one of the atomic numbers 57-71;
the steel composition fulfills the following condition:
Cr(eq)+Ni(eq)≤30;
where
Cr(eq)=Cr+2A1+1.5(Si+Nb+Ti)+Mo+0.5W; and
Ni(eq)=Ni+10(C+N)+0.5(Mn+Cu+Co); and
wherein the steel has at least 35 vol-% martensite structure.
2. The steel according to claim 1 , wherein Al is 2.6-5.0 wt. %.
3. The steel according to claim 1 , wherein Co≤ 0.1 wt. %.
4. A heat exchanger structural component comprising the steel according to claim 1 .
5. The heat exchanger component according to claim 4 , wherein heat exchanger structural component is a heat exchanger (HX) tube.
6. The heat exchanger component according to claim 4 , wherein heat exchanger structural component is a steam generator (SG) tube.